Surface Spin Waves Research Articles

Breaking Surface-Plasmon Excitation Constraint via Surface Spin Waves.

Surface plasmons in two-dimensional (2D) electron systems have attracted great attention for their promising light-matter applications. However, the excitation of a surface plasmon, in particular, transverse-electric (TE) surface plasmon, remains an outstanding challenge due to the difficulty to conserve energy and momentum simultaneously in the normal 2D materials. Here we show that the TE surface plasmons ranging from gigahertz to terahertz regime can be effectively excited and manipulated in a hybrid dielectric, 2D material, and magnet structure. The essential physics is that the surface spin wave supplements an additional freedom of surface plasmon excitation and thus greatly enhances the electric field in the 2D medium. Based on widely used magnetic materials like yttrium iron garnet and manganese difluoride, we further show that the plasmon excitation manifests itself as a measurable dip in the reflection spectrum of the hybrid system while the dip position and the dip depth can be well controlled by an electric gating on the 2D layer and an external magnetic field. Our findings should bridge the fields of low-dimensional physics, plasmonics, and spintronics and open a novel route to integrate plasmonic and spintronic devices.

Dipolar induced nonreciprocal magnon hybridization in FeNi/YIG bilayers

We investigated the magnon hybridization behavior in FeNi films, which were deposited on the yttrium-iron garnet (YIG) films by using Brillouin light scattering. Nonreciprocal magnon hybridizations have been detected not only on the mode densities but also the dispersion relations. The perpendicular standing spin wave mode confined in the thickness direction hybridized with the top surface magnetostatic surface spin wave at smaller wave vectors range while hybridized with the bottom surface mode at larger wave vectors range. The dipolar interaction between the FeNi layer and the YIG layer should be the main reason for the nonreciprocal hybridization of the two modes in the FeNi layer. The nonreciprocal hybridization characteristics of FeNi/YIG double-layer magnetic films enrich the nonreciprocal magnon hybridization system and might have potential application in constructing spin wave-based devices.

Investigation of Mode-Induced Spin Wave Transmission Blockage by In Situ Nanoscale Grooves.

In the pursuit of advancing spin-wave optics, the propagation of magnetostatic surface spin-waves is investigated in a uniform permalloy waveguide with in-situ nanopatterned grooves created through Atomic Force Microscopy nanolithography and Focused Ion Beam etching. The study unveils that the introduction of narrow constrictions and grooves leads to a non-monotonic reduction of the transmitted spin-wave signal intensity as the spin-wave pathway is shrinked. The remarkable feature that a stronger signal extinction is obtained for a narrow groove compared to a spin-waveguide interrupted by a full gap, where only inefficient transport through dipolar coupling is allowed, is highlighted. Combining experimental and numerical analyses, the intricate interplay between spin-wave diffraction and reflection at the waveguide edges is unraveled, being at the origin of a transverse-mode variation responsible for the signal extinction when detected using coplanar antennas. The findings offer insights into the controllable manipulation of detected spin-wave intensity, thereby opening promising avenues for the improvement of spin-wave switches and interferometers, and for the nanopatterning of graded indexmagnonics.

Erratum: Symmetry of the coupling between surface acoustic waves and spin waves in synthetic antiferromagnets [Phys. Rev. B 109 , 104416 (2024)

Erratum: Symmetry of the coupling between surface acoustic waves and spin waves in synthetic antiferromagnets [Phys. Rev. B <b>109</b> , 104416 (2024)

Coherent surface acoustic wave–spin wave interactions detected by micro-focused Brillouin light scattering spectroscopy

We investigated the interaction of surface acoustic waves and spin waves with spatial resolution by micro-focused Brillouin light scattering spectroscopy in a Co40Fe40B20(10 nm) ferromagnetic layer on a LiNbO3-piezoelectric substrate. We experimentally demonstrate that the magnetoelastic excitation of magnons by phonons is coherent by studying the interference of light scattered off generated magnons and annihilated phonons. We find a pronounced spatial dependence of the phonon annihilation and magnon excitation, which we map as a function of the magnetic field. The coupling efficiency of the surface acoustic waves (SAWs) and the spin waves is characterized by a magnetic field-dependent decay of the SAWs amplitude.

Symmetry of the coupling between surface acoustic waves and spin waves in synthetic antiferromagnets

Symmetry of the coupling between surface acoustic waves and spin waves in synthetic antiferromagnets

Nonlinear magnonic coupler using backpropagating surface spin waves

We investigated a spin-wave propagation in a magnon-crystal structure formed from two lateral microwaveguides separated by a one-dimensional antidot array. The mechanisms of control of the backpropagating regime of the surface spin waves both with geometry tuning and with power level variation in the case of in-plane magnetization are investigated by the method of micro-magnetic modeling and the experimental method of Brillouin light scattering spectroscopy. It was shown that for the case of spin-waves propagation through the isolated channels the shape anisotropy in the coupling region can be tuned effectively by a variation of the distance between the channels. The regime of nonlinear switching of the signal and backward propagation was observed in microwave and Brillouin spectroscopy measurements. The proposed effect of the signal separation manifests itself in the spatially and frequency-selective regimes of spin-wave propagation. Proposed spin-wave coupler opens an alternative way for the design of the functional interconnections of spin-wave based units in the planar magnonic networks.

Real-time monitoring of breath biomarkers using magnonic wireless sensor based on magnetic nanoparticles

In this paper, an innovative device with gas remote-sensing capability is proposed, which is based on the interaction between magnetic nanoparticles and gases associated with exhaled breath biomarkers that can have a metabolic origin. Magnetite (Fe₃O₄) nanoparticles of around 30 nm have been used. The gas molecules adsorbed on surface modulate the magnetization of the nanoparticles and magnetostatic surface spin waves (MSSW) propagated on an yttrium iron garnet (YIG) thin film are used to detect this modulation by the induced frequency shift. The optimization of the remote gas sensor has been carried out through simulations of a magnetic model. Simulations show the feasibility of developing a high-performance remote sensor by encapsulating the nanostructures in a polytetrafluoroethylene (PTFE) tube and detecting part per million changes in their magnetization. The results show the possibility of developing new, inexpensive, reusable, contactless magnetic gas sensors employing spin waves as transductor. The developed sensor shows a high sensitivity and selectivity to concentrations as low as 50 ppm of different breath biomarkers.

Formirovanie polos nepropuskaniyaspin-volnovogo signala v meandrovykh strukturakh iz ZhIG

A meander waveguide made of an yttrium iron garnet (YIG) film with variation of the profile is studied with a view to the possible control of band bands for surface spin waves (SSWs). The finite element method is used to determine the control mechanism of forbidden band gaps in thin YIG films. The electromagnetic problem is solved, and the dispersion characteristics of spin waves are plotted for various geometrical parameters of the meander. The nature of the change in the frequency ranges of Bragg forbidden band gaps is studied in detail depending on the profile of the meander. It is demonstrated that a three-dimensional spin-wave structure with broken translational symmetry that uses vertical spin-wave transport provides an information signal transmission in a three-dimensional configuration of magnonic networks.

Excitation and modulation of exchange spin waves in CoFeB films

Spin waves in nanostructures have great potential to be future spintronic information carriers. Here, we report the excitation and modulation of exchange spin waves in Co20Fe60B20 (CoFeB) films by varying magnetic anisotropy. In a 50 nm-thick CoFeB film, the effective excitation of perpendicular standing spin waves (PSSWs) is achieved due to the uniaxial anisotropy induced by oblique sputtering. Additionally, patterning the films into a periodic array of rectangles enables the excitation of both exchange-dominated surface spin waves and PSSWs, with the modulation of spin waves achievable by altering the length–width ratio of the rectangle. It is worth noting that PSSWs are present in the easy axis, whereas surface spin waves are observed in the hard axis, emphasizing the significant influence of shape anisotropy on spin waves. Furthermore, we demonstrate the existence of PSSW in a CoFeB/Pb(Mg1/3Nb2/3)O3-Pb0.7Ti0.3O3 (PMN-PT) multiferroic heterostructure. The resonance field of PSSW can be shifted by applying electric fields, which originates from the strain anisotropy driven by the piezoelectric effect. These findings are expected to provide valuable insights for the development of energy-efficient spintronic devices and high-frequency data processing systems.

Relationship between the spin wave distribution across a ferrite plate thickness and the directions of wave’s group and phase velocities

The general nonreciprocal properties of surface and backward spin waves in a tangentially magnetized ferrite plate are investigated. It is established the rule that determines interconnection between the spin wave localization over the ferrite plate thickness and the directions of group and phase velocities of the wave.

Antiferromagnetic magnon spintronic based on nonreciprocal and nondegenerated ultra-fast spin-waves in the canted antiferromagnet α-Fe2O3.

Spin-waves in antiferromagnets hold the prospects for the development of faster, less power-hungry electronics and promising physics based on spin superfluids and coherent magnon condensates. For both these perspectives, addressing electrically coherent antiferromagnetic spin-waves is of importance, a prerequisite that has been so far elusive, because, unlike ferromagnets, antiferromagnets couple weakly to radiofrequency fields. Here, we demonstrate the detection of ultra-fast nonreciprocal spin-waves in the dipolar exchange regime of a canted antiferromagnet using both inductive and spintronic transducers. Using time-of-flight spin-wave spectroscopy on hematite (α-Fe2O3), we find that the magnon wave packets can propagate as fast as 20 kilometers/second for reciprocal bulk spin-wave modes and up to 6 kilometers/second for surface spin-waves propagating parallel to the antiferromagnetic Néel vector. We lastly achieve efficient electrical detection of nonreciprocal spin-wave transport using nonlocal inverse spin-Hall effects. The electrical detection of coherent nonreciprocal antiferromagnetic spin-waves paves the way for the development of antiferromagnetic and altermagnet-based magnonic devices.

Reconfigurable bandpass filter using Ce-doped YIG ferrites for wideband applications

Integration of compact, tunable, low-cost monolithic microwave integrated circuit-based bandpass filters on a semiconductor substrate has been a persistent requirement in the communication industry. In the present investigation, a compact reconfigurable bandpass filter is fabricated using a double T-transducer based on the phenomena of magnetostatic surface spin waves (MSSWs). The Ce-doped Bi0.1YIG 500 μm thick disks with cerium concentration in the range of 0.2–1.0 provide the path for the propagation of MSSWs. The operating frequency for this device extends from S to X band Rogers RT/duroid® substrate, which is used for planar microstrip filter design, fabrication, and testing for practical applications. The effect of the coupling gap between the two transducers was optimized using appropriate choice of lumped components to improve the performance of the filter. The best coupling was observed for 1.2 mm coupling gap. The simulated and experimental results confirm the lowest insertion loss of −1.24 dB. The operating frequency shows a large tunability of 132.3% with a relatively small bias field of 0.3–2.1 kOe. The promising characteristics of bandpass filters such as low passband insertion loss, narrow bandwidth, high bandpass reflection coefficient, and high band-stop rejection were achieved by varying the Ce concentration in YIG samples.

Unidirectional microwave transduction with chirality selected short-wavelength magnon excitations

Nonreciprocal magnon propagation has recently become a highly potential approach of developing chip-embedded microwave isolators for advanced information processing. However, it is challenging to achieve large nonreciprocity in miniaturized magnetic thin-film devices because of the difficulty of distinguishing propagating surface spin waves along the opposite directions when the film thickness is small. In this work, we experimentally realize unidirectional microwave transduction with sub-micrometer-wavelength propagating magnons in a yttrium iron garnet (YIG) thin-film delay line. We achieve a non-decaying isolation of 30 dB with a broad field-tunable bandpass frequency range up to 14 GHz. The large isolation is due to the selection of chiral magnetostatic surface spin waves with the Oersted field generated from the coplanar waveguide antenna. Increasing the geometry ratio between the antenna width and YIG thickness drastically reduces the nonreciprocity and introduces additional magnon transmission bands. Our results pave the way for on-chip microwave isolation and tunable delay line with short-wavelength magnonic excitations.

Experimental Observation of Flat Bands in One-Dimensional Chiral Magnonic Crystals.

Spin waves represent the collective excitations of the magnetization field within a magnetic material, providing dispersion curves that can be manipulated by material design and external stimuli. Bulk and surface spin waves can be excited in a thin film with positive or negative group velocities and, by incorporating a symmetry-breaking mechanism, magnetochiral features arise. Here we study the band diagram of a chiral magnonic crystal consisting of a ferromagnetic film incorporating a periodic Dzyaloshinskii-Moriya coupling via interfacial contact with an array of heavy-metal nanowires. We provide experimental evidence for a strong asymmetry of the spin wave amplitude induced by the modulated interfacial Dzyaloshinskii-Moriya interaction, which generates a nonreciprocal propagation. Moreover, we observe the formation of flat spin-wave bands at low frequencies in the band diagram. Calculations reveal that depending on the perpendicular anisotropy, the spin-wave localization associated with the flat modes occurs in the zones with or without Dzyaloshinskii-Moriya interaction.

Nonreciprocal transmission of magnetoacoustic waves in compensated synthetic antiferromagnets

We investigate the interaction between surface acoustic waves (SAWs) and spin waves (SWs) in a Pt/Co($2\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$)/Ru($0.85\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$)/Co($2\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$)/Pt compensated synthetic antiferromagnet (SAF) composed of two ferromagnetic layers with equal thicknesses separated by a thin nonmagnetic Ru spacer layer. Because of the combined presence of interlayer dipolar coupling fields and interfacial Dzyaloshinskii--Moriya interaction (iDMI), the optical SW mode shows a large nondegenerate dispersion relation for counter-propagating SWs. Due to resonant SAW-SW interaction, we observe a nonreciprocal SAW transmission in the prepared piezoelectric/SAF hybrid device. We demonstrate that the nonreciprocity of the SAW transmission in symmetric SAFs with equal thicknesses of the magnetic layers can show a substantially different characteristic behavior in comparison to asymmetric SAFs or magnetic single layers with iDMI. For the prepared SAF, the nonreciprocal shift of the magnetoacoustic resonance fields and the magnetoacoustic SW excitation efficiency depend on the external magnetic field sweep direction. For one magnetic field sweep direction and angle of the magnetic field, the resonance fields of the waves propagating in one direction are larger than for the waves propagating in the opposite direction. In addition, the magnitude of the nonreciprocal field shift is at minimum if the external magnetic field is aligned perpendicular to the SW propagation direction. The experimental results are in agreement with a phenomenological SAW-SW interaction model.

Surface properties of ferromagnetic films and spin wave modes

Ferromagnetic films are a fundamental platform in Magnonics, the area that studies spin wave propagation and its possible applications. These films have been studied for a long time experimentally and theoretically, either individually or as parts of multifilms structures. The present study delves into an issue of interest that remains to be studied in detail, which is the relation between the surface properties of these films and the spin wave propagation in them. The main idea of this work is that the frequencies of spin waves may be determined experimentally with precision and through their relation with surface properties one may theoretically validate and derive the main parameters of models that describe the behavior of the surfaces. Several parameters may be changed in the process of testing the relation between surface properties and spin waves, like an applied magnetic field orientation and strength, the angle of in-plane spin wave propagation, etc. This study uses a continuum micromagnetic model for the description of the magnetization dynamics, in this case, the surface properties enter through effective boundary conditions. Three models of surface properties are studied: uniaxial surface anisotropy, the latter combined with bulk uniaxial anisotropy, and surfaces with Dzyaloshinskii-Moriya interactions (DMI). In general, the boundary conditions affect the equilibrium magnetization in boundary layer regions close to the surfaces: an asymptotic analysis predicts their penetration lengths for reasonable surface anisotropies. For very thin films, this is quite relevant since the boundary layers are of the order of the film thickness, we propose this as a practical way to define what may be considered a very thin film. Effective physical parameters of thin films and very thin films clearly depend on the surface properties. The main effects of the surfaces on spin waves occur for angles of inclination of the applied magnetic field close to perpendicular to the plane, and they may be of significant magnitude. Several different numerical methods were used to solve for the spin waves, in the context of an orthogonality equation method.

Spin wave selection in an ensemble of laterally and vertically coupled iron-yttrium garnet microwaveguides

Numerical micromagnetic modeling used to study the modes of propagation of spin waves and processes of power transfer in the considered arrays of microwaves in the configuration corresponding to excitation in two central channels of one of the layers of surface and inverse bulk magnetostatic spin waves is conducted. It is shown that the proposed structure performs the functions of spatial-frequency signal selection, the efficiency of which depends on the mutual orientation of the submagnetization field and the direction of wave propagation.

Reconfigurable magnon interference by on-chip dynamic wavelength conversion

Spin waves (SWs), an ultra-low power magnetic excitation in ferro or antiferromagnetic media, have tremendous potential as transport less data carriers for post-CMOS technology using their wave interference properties. The concept of magnon interference originates from optical interference, resulting in a historical taboo of maintaining an identical wavevector for magnon interference-based devices. This makes the attainment of on-chip design reconfigurability challenging owing to the difficulty in phase tuning via external fields. Breaking the taboo, this study explores a novel technique to systematically control magnon interference using asymmetric wavevectors from two different SW modes (magnetostatic surface SWs and backward volume magnetostatic SWs) in a microstructured yttrium iron garnet crossbar. Using this system, we demonstrate phase reconfigurability in the interference pattern by modulating the thermal landscape, modifying the dispersion of the interfering SW modes. Thus, we manifest that such a tunable interference can be used to implement reconfigurable logic gates operating between the XNOR and XOR modes by using symmetric and asymmetric interference, respectively.

Out-of-plane Ferromagnetic Resonance and Surface Spin Wave Modes in Ni80Fe20 Film on Ripple-Patterned Sapphire Substrate

The study of surface magnetic anisotropy of magnetic films is beneficial to understanding the behaviors of films at high frequencies and further promoting their high-frequency magnetic applications. We investigated the out-of-plane ferromagnetic resonance (FMR) and surface spin wave modes in 40-nm Ni80Fe20 (NiFe) films deposited on ripple-patterned sapphire substrate with periodicity and a flat sapphire substrate by broad-band FMR technique. When measuring the FMR of the film on ripple-patterned substrate, the in-plane angle (\U0001d711 H of the external applied magnetic field was along the direction of the ripples (\U0001d711 H = 90°) and perpendicular to the ripple direction (\U0001d711 H = 0°) respectively. The spin-wave resonance spectra consisting of up to two surface spin wave (SSW) modes were observed as the external magnetic field polar angle θH varied from “in-plane configuration” (θH = 90° ) to “out-of-plane configuration” (θH = 0°). As the decrease of θH , the two surface spin excitations disappeared in sequence and further only FMR mode was observed in the region θH which was smaller than the “critical angle” θc . The θc of \U0001d711 H = 90° is found to be different from that for \U0001d711 H = 0°. The dependences of field shift vs. out-of-plane angles θH for each SSW mode were analyzed by the surface inhomogeneity model. From the model, the surface anisotropy constants Ks of films were obtained. The results show that the values of surface anisotropy constants for the two SSW modes are different. Compared with the film sputtered on flat sapphire substrate, after introducing ripple-patterned substrate, the variation of Ks is only on the order of 0.01 erg/cm2 for the film of this thickness.